The long-term goal of this work is to develop fall prevention guidelines that are protective for obese and older workers because current guidelines do not account for the special needs of these subpopulations. Two specific aims are proposed. The first aim will determine the effects of obesity and increased age on risk of slipping, tripping, and losing balance during simulated construction work. Our focus is on slips, trips, and loss of balance because they are among the most commonly reported contributing factors to falls in the workplace. This aim will also focus on realistic situations in construction work (i.e. work that has an inherent high risk for falls) that can lead to a slip, trip, or loss of balance, and that are amenable to safety guidelines to reduce fall risk. The second aim will determine the effects of obesity and increased age on balance and balance recovery after slipping and tripping. The results from both aims will improve our understanding as to why obese and older workers are at an increased risk of falls. The results can also be used by policy makers to develop revised fall-prevention safety guidelines or designs for safety that are protective for obese and older workers. This research is novel in two aspects. First, it is novel in targeting the main and interactive effects of obesity, aging, and work experience on balance in the construction industry. While the main effects of aging on balance have been studied extensively, the effects of obesity, experience, and their interaction with aging have received little attention despite the growing number of obese and obese older construction workers. Second, it includes testing under realistic working conditions so that results can be more-readily translated to safety guidelines and/or designs for safety to reduce the risk of falls in obese workers. This research has the added benefit that, while focused on construction, several of the results are applicable to other occupational sectors. PUBLIC HEALTH RELEVANCE: Falls are a significant cause of morbidity and mortality among workers. Demographic trends in the United States indicate a growing number of obese and older workers, but fall prevention safety guidelines do not account for the specific needs of these individuals. The work proposed here will more fully characterize the effects of obesity and age on balance and risk of falls, and provide data that, along with existing evidence, can be used by policy makers to develop more inclusive safety guidelines that account for the balance abilities of obese and older workers.